How to remove a Other volume in HD which I cannot access

amandafromwr wrote:

Hi I partitioned my MacHD disk using Maverick, thinking I would use it to put on an additional operating system then changed my mind and updated my mac to Catalina.

Right, this is the beginning of the new normal.

ref: About the read-only system volume in macOS Catalina - Apple ...

About the read-only system volume in macOS Catalina - Apple Support

Add, delete, or erase APFS volumes in Disk Utility on Mac

You can see even more in your DiskUtility>View>Show All Devices...

(all Volumes 'share' space with the Container there is no penalty.)

or

from the Terminal.app copy and paste:

diskutil list internal

Terminal User Guide for Mac - Apple Support

That's the new normal for macOS.

Look closely at the icons representing each volume. One indicates the volume is the macOS system volume. It's a read only volume that is the secure location for the OS.

The other is the data volume that on which your user account and files reside.

Finder never displays both volumes separately. Disk Utility and Terminal can allow you to visualize each.

The free space in the drive device is available to either volume dynamically. The OS manages this automatically, magically. The storage is not lost to either and there is no ability or reason to recover it in your case.

You cannot delete this. This is a part of your AFPS file system. My disk utility shows it exactly the same and I installed a clean copy of High Sierra on that one, it is a brand new SSD